Recirculation of exhaust gas into the air intake stream of an internal combustion engine is well known, both for spark-ignited (SI) engines and for compression-ignited (CI) engines. Such recirculation requires a rugged, dependable, precision valve, typically a poppet valve, disposed in a cross-over between an engine's exhaust system and intake system. In many prior art automotive uses, an EGR poppet valve is actuated by a linear solenoid attached to the valve stem. However, a rotary cam driven by an electric motor is also a well known actuation means, especially for diesel-powered automotive applications in Europe. Such usage is expected to become more prevalent world wide.
For ease of presentation, the terms “rotary cam” and “rotary EGR valve” as employed herebelow should be taken to mean any arrangement wherein the linear action of the valve stem is controlled by the rotary motion of an eccentric coupled in some fashion to the valve stem.
Rotary EGR valves have become especially popular because of the generally high force margins they enjoy over other designs, and particularly because of inherent significant mechanical advantages through gearing and camming. Typically, this genre of valves is actuated in both opening and closing directions, as well as in parked (closed) position during engine operation when EGR flow may not be desired.
A disadvantage of such actuation is inherently high and sustained forces imposed on the valve actuation train that can prove detrimental for long-term wear, including grooving of the valve head, wear of the valve seat, and degradation of the interface between the cam and its roller follower on the valve stem. Such wear can result in high break-loose forces and “kinking”, leading to poor controllability in the just off-parked position.
Of course, these considerations pertain not only to rotary EGR valves but also to all poppet valves actuated by powerful actuators, whether rotary cams or linear solenoids.
What is required is a means for attenuating the seating force of a poppet valve without compromising the timing or the closing reliability of the valve.
It is a principal object of the present invention to attenuate the seating force of a poppet valve.